The present invention relates to a rubber member for rubber-sprung rail wheels in which the rubber member is disposed under prestressing in an annular gap between concentric wheel parts. The rubber member has an opening provided between its opposite faces bearing against the wheel parts and a flexible current bridge being disposed in the opening.
The present invention also relates to a rubber-sprung rail wheel using such a rubber member.
In a prior an rubber-sprung rail wheel, peripherally distributed radially prestressed rubber members are disposed in an annular gap formed by a wheel rim and a wheel tire of the rail wheel. When the rubber member is expanded or unstressed, the opening therein has a circular cross-section which in practice is only slightly larger than the diameter of the flexible current bridges. The circular cross-sections are deformed to oval under the radial prestressing of the rubber members. As a result, the free spaces for movement of the flexible current bridge are limited during retraction and expansion, more particularly having regard to the imprecision of its position, and this may lead to breakages and to a reduction in the effectiveness of the current bridge. In modern high-speed trains, in which the rubber members are subjected to an increased change of load up to 25 load modulations per second, this leads to a reduction in the required service life of approximately 5.times.10.sup.8 load modulations. In the case of tramcars, with a smaller number of load modulations, comfort is adversely affected with respect to a required high springing deflection member.
It is an object of the invention to improve the durability of a rubber member having a current bridge and also to improve the service life of a rubber-sprung rail wheel having a rubber member having a current bridge.
This problem is solved by a rubber member that has an opening with an oval cross-section in the flexible zone of the current bridge when the rubber member is in its expanded or unstressed state. The problem is also solved by a rail wheel using such a rubber member where the annular gap is formed by concentric parts, namely a wheel rim of the wheel body and a wheel tire. The rail wheel may have a plurality of peripherally distributed radially prestressed rubber members disposed in the annual gap, of which at least one has the current bridge.
According to the present invention the oval cross-section of the opening may be deformed to a circular shape, thus creating an optimum space for current bridge movement during expansion and retraction. The result is an increase in the service life of the rubber member having a current bridge and, therefore, also the service life of the wheel rail equipped with such a rubber member. If a rubber member should have a number of openings furnished with current bridges, preferably all the openings should have an oval shape when in the expanded or unstressed shape.
According to one feature of the present invention, preferably the oval cross-section is elliptical. Preferably the ratio between the maximum diameter of the oval cross-section and the minimum diameter is 1.25-1.35/1.
In one embodiment, the opening for the current bridge has at each of its ends a widened portion in which a contact shoe that is connected to the current bridge may be disposed. The widened portion preferably has an oval cross-section and is offset by 90 degrees in relation to the axis of the oval cross-section of the opening. Preferably the minimum diameter of the widened portion is 0 to 20% larger than the maximum diameter of the central zone of the opening.